use strict;
use warnings;
my %server_hash = ( 
  'server1' => ['cluster1',0], 
  'server2' => ['cluster1',0], 
  'server3' => ['cluster2',0], 
  'server4' => ['cluster2',0] );

my %cluster_totals = ();
foreach my $this_server(keys %server_hash) {
  $server_hash{$this_server}->[1] = getCPUUtilization($this_server);
  $cluster_totals{$server_hash{$this_server}->[0]} += $server_hash{$this_server}->[1];
}
foreach (keys %cluster_totals) {
  print "Cluster: $_ \t $cluster_totals{$_}\n";
}